Guys, you're totally out of it. A FO flying a multi-crew aircraft can log all time as P1/US where they are the PF, providing that entry is signed by the P1 or the Chief Pilot certifies the logbook confirming all P1/US time.
You can still get that, but you still need 100hrs of real PIC, not P1/US, to get your ATPL
100 hours P1 is a requirement to commence a CPL training course, so not really one to worry about.